We shall continue exploring the host- and parasite factors relevant to the pathogenesis of schistosomiasis and of granuloma formation, with special emphasis on: Direct cytotoxic effects of schistosome eggs on host liver cells, as mainfested in mice with deficient T-lymphocyte function, and in mouse liver parenchymal cells in tissue culture monlayers, and on the modulatory influence of egg-directed antibody during the acute stage of schistosomiasis. Comparative cellular and morphological characteristics and fibrous sequelae of schistosome granulomas in T-cell deficient, normal, and T-cell-adjuvant (lentinan) immunopotentiated mice, respectively; similar comparisons will be effected between/schistosome species and strains of differing pathogenicity (S. mansoni, S. japonicum and S. mekongi). The immunopathogenesis of diffuse fibrous lesions in S. jeponicum infection of hamsters and rabbits, such as portal fibrosis and bilharziomas. The immunopathogenesis and fine structure of the Hoeppli phenomenon in S. japonicum and S. mekongi infected hosts. The in vivo effects of eosinophilic granulocytes on schistosome egg viability and on antigen catabolism. Our aim is to better define the factors which modulate the cell populations and morphological features of schistosome egg granulomas, and to better understand the pathogenic consequences of defective, normal, and excessive host immunological reactivity against schistosome eggs.